Ceramic tiles can be decorated by digital printing with either (a) pigmented or (b) soluble salt based digital inks.
Pigmented digital inks for ceramic tile use metal, mixed metal oxides, metal-oxide, metal-sulfide, or metal-selenide particles as the ink chromophores. These pigment particles are dispersed within a liquid matrix to produce the inks. These pigmented inks are digitally printed to the surface of a glazed tile preferably, but not exclusively, prior to firing in a ceramic kiln. The purpose of the glaze layer is functional, i.e. waterproof, and aesthetic. Typical kiln temperatures for this decorative technique are 1000 to 1190 Celsius (° C.). No post-processing is required after the kiln firing step.
Soluble salt digital inks for technical porcelain ceramic tile use soluble metal compounds, rather than dispersed pigment particles, that convert into pigments by oxidation and/or reaction with other compounds in the green body during the firing in the kiln. The soluble metal compounds can be organometallic in nature, such as metal carboxylates, citrates, β-diketonates, cyclopentadienates, pyrazolates, imidazolates, naphthanate, glutonate, formate, thiocarboxylates, dithiocarboxylates, maleates, organophosphorus compounds, organosulfur compounds, and others, or purely inorganic in nature, such as metal chlorides, sulfates, sulfites, phosphates, phosphites, nitrates, nitrites, halides, perchlorates, metal oxoanions, and others. The metal salts are dissolved in a solvent, such as water and/or organic solvents, to produce the inks. The ink solutions are applied to the surface of an unglazed green tile porcelain body preferably, but not exclusively, using digital printer and print head technology. A green tile is a tile that has been formed, such as by a hydraulic press, but not fired and strengthened in a kiln. Typical application quantities are 15-50 grams per square meter (g/m2) of ink per color. Additional solvent is often applied after ink application to help the ink penetrate at least 1 millimeter (mm) into the tile body. This additive is often referred to as a penetration or diffusion additive. The tile is fired in a kiln at porcelain temperatures (1190-1230° C.). After firing, the tile undergoes a polishing step, resulting in a glossy decorated technical porcelain tile.